viktorklang

    //isValid = predicate/constraint
    abstract class Type[T](val isValid : (T) => boolean)
    {
        //X is the reference type
        final protected[Type] case class X[T] (val value : T) {
            override def toString = Type.this.getClass.getSimpleName + "(" + value + ")"
        }

        //Type is the alias for X[T] that we expose to the outside world
        type Type = X[T]